Toner sealants are used, for example, for the sealing of the toner hoppers of laser printers, copiers, and the like. The ink toner hoppers are sealed with the toner sealants so as to prevent the extraleakage of the toner, which is a fine powder. Air sealants are used, for example, in doors for conditioners provided in various automotive air ducts. These air sealants function to seal the air flow selector valves disposed in ducts for introducing air conditioned with respect to temperature, humidity, etc. into the cabin for the purpose of ventilation and air conditioning.
Polyurethane foams produced using a polyester polyol as a raw material (hereinafter referred to as "ester foams") are soft and have low air permeability, reduced permanent compression set, and excellent durability. Due to such advantages, these polyurethane foams have conventionally been frequently used as various sealants. For use in applications such as those shown above, sealants are required to also have excellent resistance to ozone deterioration. The ester foams are exceedingly superior in this point to polyurethane foams produced using a polyether polyol as a raw material (hereinafter referred to as "ether foams").
However, even the ester foams, when used as either toner sealants or air sealants, have a problem that the foams suffer cell wall breakage and a considerable increase in air permeability during long-term exposure to ozone contained in a slight amount in the atmosphere and, as a result, come to malfunction as sealants. The ester foams have another problem that they deteriorate as a result of the hydrolysis of ester bonds, which are attributable to the polyester polyol used as a major raw material.
The ester foams or the ether foams have hitherto been used as sealants for doors for automotive conditioners. Although the ester foams have excellent sealing ability at the initial stage, the foams deteriorate as a result of their hydrolysis in several years when they are used under the practical circumstances. In some serious cases, the foams break down into powders by touching them. As a result, the sealing ability of the foam remarkably decreases. For coping with the problem due to the hydrolysis, the ether foams started to be used in recent years. Although it has been confirmed that the ether foams have a life at least three times longer than that of the ester foams because the ether foams have reduced susceptibility to hydrolysis, the ether foams have another problem that they tend to cause ozone deterioration as compared with the ester foams.
Recently, air sealants for use in the doors for automotive conditioners are frequently required to have long-term durability for, e.g., 10-year warranty, because of the supposed severe environment in which the sealants will be used. Accordingly, the problems of the hydrolysis of the ester foams and the ozone deterioration of the ether foams become more serious.
In recent years, size reduction in toner particles for use in copiers and the like is progressing with the trend toward finer and color images. Because of this, strongly acidic or alkaline resins have come to be frequently used as resin ingredients for preparing colorant-containing toners, in place of conventionally employed neutral resins. As a result of this resin pH change, the hydrolysis of ester foams has come to be accelerated, and there are an increasing number of cases where ester foams come to malfunction as sealants in relatively short time periods.